The field of the present invention is method and apparatus for supplying liquid lubricant from a reservoir thereof to a place of utilization. More particularly, the present invention relates to method and apparatus for supplying liquid lubricant to the bearings of a combustion turbine engine.
Present Federal Aviation Administration (FAA) regulations require that a combustion turbine engine, whether of turboshaft, turboprop, turbofan or turbojet configuration, be able to continue engine operation for a period of no less than thirty seconds after the loss of oil flow from the main oil supply system to the engine bearings without suffering engine damage. This thirty second grace period provides a time during which the pilot of the aircraft may decide, for example, whether a take-off may be aborted following the loss of the main engine oil supply system. In the event that the take-off cannot be aborted, the thirty seconds of engine operation without damage provides at least a portion of the operating time which is required to complete the take-off and arrange for a safe landing at the air field. With present engine designs this grace period of thirty seconds is provided by overdesign of the engine bearings so that they may operate without their normal lubricant coolant flow, utilizing whatever lubrication may remain in the bearing after the cessation of this lubricating and cooling flow to sustain bearing operation without damage.
Conventional proposals have been made to supply the bearings of a turbine engine with emergency lubricating oil from a main oil tank which is kept under pressure during normal engine operation and, in the event of failure of the main oil pump, flow is allowed via an alternative flow path from the oil tank under internal pressure to the bearings through a check valve. This conventional proposal is undesirably complex and is subject to substantially the same risk of damage as is the main oil supply system because it uses the main oil supply tank.
Alternative conventional emergency lubrication systems for turbine engines have variously proposed the use of aspirating nozzles or an aerosol generating apparatus to carry emergency lubricating oil to the engine bearings along with a cooling air stream. However, these proposals also suffer from undue complexity and risk of damage in common with the main oil supply system. Yet another alternative proposal has been to provide an accumulator in an oil supply line to the engine bearings. The accumulator receives a collapsible bladder normally pressurized internally to a level lower than the oil supply from the main lubrication system. Upon the failure of the main lubrication system, the accumulator in conjunction with a check valve preventing backflow to the main lubrication system supplies oil to the bearings as the bladder is expanded by its internal pressure.
Each of these conventional emergency lubrication supply systems is recognized as suffering from one or more of several deficiencies. These emergency lubrication systems are exceedingly complex in many cases, they are therefore inordinately expensive, and are also subject to failure in common with the main lubrication system or because of modes of failure related uniquely to the emergency lubrication system itself. It is recognized, therefore, as desirable that turbine engines be provided with an emergency lubrication system which is simple in structure, inexpensive, and not subject to many of the causes of failure which may befall the main engine lubrication system.
Yet another area of recognized problem in the turbine engine field is that of supplying bearing lubrication to expendable engines such as those designed for short term operations of weapon-carrying vehicles or target drones. As will be appreciated, because these engines are expendable, their price and the cost of associated components and systems must be kept as low as possible. Also, these lubrication supply systems must be extraordinarily reliable because in many cases the target drone or weapons-carrying vehicle will be expected to endure storage for a number of years prior to its operation, after which its operation without preparatory field service is expected.